Thiocyanate transformation mechanisms based on microbial metabolic and treatment technologies for thiocyanate-containing wastewater: A critical review

Thiocyanate (SCN⁻), a persistent and toxic pollutant in industrial wastewaters, threatens ecosystems via mechanisms like cytochrome oxidase inhibition and bioaccumulation. Microbial degradation occurs through dual metabolic pathways: autotrophic sulfur-oxidizing bacteria (e.g., Thiobacillus) utilize SCN⁻ as an electron donor, while heterotrophic bacteria (e.g., Pseudomonas) metabolize it as a sulfur or nitrogen source, predominantly via carbonyl sulfide (COS) and cyanate (CNO) intermediates yielding sulfate and ammonium. Optimized aerobic biological reactors, such as sequencing batch reactors (SBR) and moving bed biofilm reactors (MBBR), have demonstrated high SCN⁻ removal efficiencies (>95 %) through strategies like oxygen gradient control and biofilm carrier optimization. However, addressing the need for more sustainable, low-carbon treatment strategies highlights the potential of anaerobic technologies. Integrated systems coupling sulfur autotrophic denitrification with Anammox offer a promising pathway for simultaneous removal of sulfur and nitrogen pollutants through metabolic coupling, significantly reducing operational costs and environmental impact. Critical challenges persist, including maintaining functional microbial community stability and mitigating nitrite (NO₂⁻) competition between the coupled sulfur and nitrogen cycles. Advancing multi-omics analyses to decode complex microbial interactions in multi-substrate environments, exploring quorum sensing regulation, and developing novel processes like thiocyanate-driven sulfur-oxidizing heterotrophic denitrification (T-SOHD) represent key future directions. These innovations are vital for driving the development of efficient and truly low-carbon solutions for industrial thiocyanate detoxification.